Methane conversion to methanol

In addition to these principal commercial uses of molybdenum catalysts, there is great research interest in molybdenum oxides, often supported on siHca, ie, MoO —Si02, as partial oxidation catalysts for such processes as methane-to-methanol or methane-to-formaldehyde (80). Both O2 and N2O have been used as oxidants, and photochemical activation of the MoO catalyst has been reported (81). The research is driven by the increased use of natural gas as a feedstock for Hquid fuels and chemicals (82). Various heteropolymolybdates (83), MoO.-containing ultrastable Y-zeoHtes (84), and certain mixed metal molybdates, eg, MnMoO Ee2(MoO)2, photoactivated CuMoO, and ZnMoO, have also been studied as partial oxidation catalysts for methane conversion to methanol or formaldehyde (80) and for the oxidation of C-4-hydrocarbons to maleic anhydride (85). Heteropolymolybdates have also been shown to effect ethylene (qv) conversion to acetaldehyde (qv) in a possible replacement for the Wacker process. 

Other metals capable of electrophilic substitution of C-H bonds are salts of palladium and, environmentally unattractive, mercury. Methane conversion to methanol esters have been reported for both of them [29], Electrophilic attack at arenes followed by C-H activation is more facile, for all three metals. The method for making mercury-aryl involves reaction of mercury diacetate and arenes at high temperatures and long reaction times to give aryl-mercury(II) acetate as the product it was described as an electrophilic aromatic substitution rather than a C-H activation [30],... 

The CH-activation of alkanes and especially of methane and their catalytic conversion to alcohols is one of the major challenges for chemists. Methane as the major part of natural gas is currently the cheapest source of hydrocarbons and the need for methanol will increase in the near future. Methane conversion to methanol would make a conveniently transportable fuel and also a new carbon source for the chemical industry. 

Direct one-stage oxidation of methane to methanol is performed by two methods catalytic and thermal. Modernization of the process of methane conversion to methanol using various catalysts is ineffective, because in this case methane conversion is usually below 13%. At the present time, methane conversion to methanol has been raised to 24% [122] however, this is still insufficient for an economic assessment of the process. Hence, thermal... 

Many other partial oxidations have been studied methane conversion to methanol and formaldehyde. 

As shown in equation (27), methanesulfonic acid can be transformed to methyl bisulfate, which is easily hydrolyzed to methanol. Hence, the synthesis of methanesulfonic acid is regarded as a methane conversion to methanol. Metal peroxides such as Ca02 catalyze the reaction of methane and fuming sulfuric acid to give methane sulfonic acid at a rather low temperature (eq. (29)) (49). 

Department of Chemical Engineering, University of Colorado, Boulder. Direct Methane Conversion to Methanol, Quarterly Status Report, October 1, 1992-December 31, 1992. Report No. DOEMC271153343, Contract No. FG2190MC27115. Washington, DC U.S. Department of Energy, 1993. 

Figure 23.7 Nondirect and direct routes of methane conversion to methanol. X stands for SO3H or OSO3H.

Cheng, J., Li, Z., Haught, M., and Tang, Y. (2006) Direct methane conversion to methanol by ionic liquid-dissolved... 

An alkane CH bond can oxidatively add to a variety of low-valent tiansi-tion metals preferentially to give the linear product, n-Pr-M-H, however, and in any subsequent functionalization, the linear product, n-PrX, is often obtained. In addition, methane activation holds promise as methane seems likely to become a more important feedstock for the chemical industry. Methane conversion to methanol or a derivative (e.g., MeOCH20Me) would make a conveniently transportable fuel. Partial oxidation such as this is particularly hard. Methanol is much more easily oxidized than methane, so classical oxidation procedures give CH2O, CO and CO2. In the CH activation route, the CH bond of methanol is not much more reactive than in methane, so the overoxidation problem is less severe. 

The issue of how hydrocarbon additives influence the selectivity of methane conversion to methanol is more complicated. Although the selectivity of methanol formation increases noticeably (Fig. 4.3), a significant portion of this gain can be associated with the conversion of the added alkane. 

In principle biomass is a useful fuel for fuel cells many of the technologies discussed above for using biomass as a fuel produce either methane or hydrogen directly and as highlighted below synthesis gas production from biomass for conversion to methanol is an attractive option. Cellulose-based material may be converted to a mixture of hydrogen (70% hydrogen content recovered), CO2 and methane by high-temperature treatment with a nickel catalyst. 

Fig. 20. The steady-state concentrations of carbon dioxide (top), water (center), and methane (bottom) as functions of the C02/C0 ratio in the feed gas at 225-250°C, 75 atm total pressure, and GHSV 5000 hr 1 (56) (-O-) 250"C, (—V—), 235°C, (- -) 225 C. Conversions to methanol are given in Fig. 19. From Ref. 55.

Two examples of low temperature, catalytic, methane oxidation by hydrogen peroxide should be included in this section. The first involves conversion to methanol using cis-[Ru(2,9-dimethyl-l,10-phenanthroline)(solvent)2](PF6)2 as the catalyst [39]. A ruthenium-oxo species has been proposed as the C-H activating species. In the second report, conversion of methane to methyl hydroperoxide is claimed [40]. The catalyst is a combination of [NBuJ V03 and pyrazine-2-carbox-ylic acid. While the mechanism is uncertain, the actual oxidant is believed to be dioxygen with HO derived from hydrogen peroxide acting as the initiator. 

Reforming of methane to synthesis gas for subsequent conversion to methanol or production of gasoline and diesel fuels from methanol via Mobil technology is commercially available. 

MMO, one of the members of diiron-containing metalloenzyme family, is an enzyme that catalyzes methane oxidation reaction, i.e. conversion of the inert methane molecule to methanol [15]. During this reaction two reducing equivalents from HAD(P)H are utilized to spht the 0-0 bond of O2. One O atom is reduced to water by 2-electron reduction, while the second is incorporated into the substrate to yield methanol ... 

NO was used as an oxidant. Methane conversion and methanol selectivity reached 6% and 88%, respectively, after UV irradiation for 3 h. As shown in Figure 18.9, the yield of methanol increases with an increase in the V content up to 0.6 wt%, and then decreases with a further increase in the V content. The observed good correspondence between the yield of methanol and the intensity of the photoluminescence indicates that the isolated tetrahedral oxide species act as active sites for the photocatalytic oxidation of methane with NO into methanol. 

C02-selective polymeric membranes (cardopolymers, FSCs), CMS, mixed matrix, or biomimetic materials are potential membrane materials for this application. The purified methane can then be compressed to 300 bar and stored in tanks for fuel in the transport sector or for conversion to methanol used for FCs. 

Figure 2.39 Equilibrium conversion to methanol, DME and methane as a function of temperature and discrete values of pressures 10 and 50 bar. Feed methanation H2/C0=3, methanol and methanol/DME H2/CO=2.

Although our knowledge on the partial oxidation of methane to methanol was improved, there remains a need for better catalytic materials with a reduced activity for consecutive overoxidation of primarily formed methanol to carbon oxides. Alternatively, approaches aimed on methane conversion to kinetically more stable methanol derivatives may be of interest for further research. 

In contrast to methane conversion to C2 hydrocarbons (Section 23.2) and methanol (Section 23.3), methane conversion to acetic acid is still in its infancy. This approach is by no means competitive to the present Monsanto technology. Successful methane conversion will require novel significantiy more active catalysts. 

Methane reacts to methanol and CO at 450°C over Cr20s in batch reactors and reaction times up to 40 min. The reproducibility was limited due to the small reactor size (1.26 ml). At 10% methane conversion, methanol selectivity reached 40%. Compared to a gas-phase reaction, conversion was less but the yield was higher. Continuous partial oxidation of methane with catalysts Cr203/Al203 and Mn02/Ce02 at 400 75°C led to the formation of methanol, formic acid and other partial oxidation products. Metals Ag, Cu and Au/Ag as catalysts are also able to convert methane (375-500°C, 220-350 bar, residence time 0.5-60 s) into methanol and formaldehyde with 50-80% selectivity at conversion below 1%. ... 

Because carbon is the limiting factor, the carbon conversion to methanol, also referred to as carbon efficiency, is an important operating parameter for overall ener efficiency. Carbon efficiency is a measure of how much carbon in the feed is converted to methanol product. There are two commonly used carbon efficiencies, one for the overall plant and one for the methanol synthesis loop. For the overall plant all the carbon-containing components in the process feedstock from the battery limits and the methanol product from the refining column are considered. For a typical plant and natural gas feedstock, an overall carbon efficiency is about 75%. The methanol synthesis loop carbon efficiency for the same plant is about 93%. The synthesis loop carbon efficiency is calculated using only the carbon in the reactive components in the makeup gas (CO and C02). Carbon in the form of methane is not considered because it is inert in the methanol synthesis reaction and is ultimately purged from the loop and burned. The carbon in the product for this calculation is that in the form of methanol in the crude leaving the methanol synthesis loop. 

The effect of pressure on the methane conversion and methanol )deld is shown in Fig. 9.16. The )deld reaches a maximmn at P = 2 atm after which it rapidly decreases, primarily due to the reduction of the methane conversion. 

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